This invention generally relates to printer apparatus and methods of manufacture and more particularly relates to a print engine frame incorporating the print engine chassis and fabricated using sheet metal reinforced with castable polymer concrete.
Pre-press color proofing is a procedure used by the printing industry for creating representative images of printed material. This procedure avoids the high cost and time required to produce printing plates and also avoids setting-up a high-speed, high-volume printing press to produce a representative sample, as a proof, of an intended image to be printed. Otherwise, in the absence of pre-press proofing, a production run may require several corrections and be reproduced several times to satisfy customer requirements. This results in lost time and profits. By utilizing pre-press color proofing, time and money are saved.
A laser thermal printer having half-tone color proofing capabilities is disclosed in commonly assigned U.S. Pat. No. 5,268,708 titled xe2x80x9cLaser Thermal Printer With An Automatic Material Supplyxe2x80x9d issued Dec. 7, 1993 in the name of R. Jack Harshbarger, et al. (Harshbarger, et al.) The Harshbarger, et al. device is capable of forming an image on a sheet of thermal print media by transferring dye from a roll of dye donor material to the thermal print media. This is achieved by applying a sufficient amount of thermal energy to the dye donor material to form the image on the thermal print media. This apparatus generally comprises a material supply assembly, a lathe bed scanning subsystem (which includes a lathe bed scanning frame, a translation drive, a translation stage member, a laser printhead, and a rotatable vacuum imaging drum), and exit transports for exit of thermal print media and dye donor material from the printer.
Although the printer disclosed in the Harshbarger, et al. patent performs well, it would be advantageous to reduce manufacturing costs for this type of printer and for similar types of imaging apparatus. In addition, reducing the overall size of such a printer would have advantages in minimizing floor-space requirements for customers. In the printer disclosed in the Harshbarger, et al. patent, a machine casting is used for the print engine chassis and this chassis, in turn, is mounted atop a metal frame. The metal frame is typically welded together and requires substantial strength to support the print engine and its writing components. Vibration compensation is required to isolate any vibration from equipment in the frame, such as fans and vacuum equipment, from interfering with the precision printhead and its translation apparatus. Rubber mountings are required between print engine chassis and frame.
The machined casting used as the frame represents significant cost relative to the overall cost of the printer. Cost factors include the design and fabrication of the molds, the casting operation, and subsequent machining needed in order to achieve the precision necessary for a lathe bed scanning engine used in a printer of this type. Castings present inherent problems in modeling, making it difficult to use tools such as finite element analysis to predict the suitability of a design. Moreover, due to shrinkage, porosity, and other manufacturing anomalies, it is difficult to obtain uniform results when casting multiple frames. In the assembly operation, each frame casting must be individually assessed for its suitability to manufacturing standards and must be individually machined. Further, castings also exhibit frequency response behavior, such as to resonant frequencies, which are difficult to analyze or predict. For this reason, the task of identifying and reducing vibration effects can require considerable work and experimentation. Additionally, the overall amount of time required between completion of a design and delivery of a prototype casting can be several weeks or months.
The combined weight of the imaging drum, motor and encoder components, and print head translation assembly components, plus the inertial forces applied when starting and stopping the drum require a frame having substantial structural strength. For this reason, a sheet metal frame, by itself, would not be considered to provide a solution.
Alternative methods used for frame fabrication have been tried, with some success. For example, welded frame structures have been used. However, these welded structures require significant expense in manufacture.
Alternatives to metal castings and welded structures have been used by manufacturers of machine tools. In particular, castable polymers, manufactured under a number of trade names, have been employed to provide support structures that are at least equivalent to castings for apparatus such as machine tool beds and optical tables. These castable polymers also provide improved performance when compared with castings, with respect to expansion/contraction due to heat and with respect to vibration damping.
To provide substitute structures for metal castings and weldments, one example of the use of a castable polymer is disclosed in U.S. Pat. No. 5,415,610 (Schutz et al.). Schutz et al. discloses a frame for machine tools using castable concrete to form a single casting of a bed and a vertical wall for a machine tool. U.S. Pat. No. 5,678,291 (Braun) and 5,110,283 (Blumi et al.) are further examples in which a castable polymer concrete is used as a machine tool bed or for mounting guide rails in machining environments. Castable polymers are also used in the machine tool environment for damping mechanisms, as is disclosed in U.S. Pat. No. 5,765,818 (Sabatino et al.) These machine tool applications use castable polymer concrete as a high-mass bed for tool support and vibration damping.
There has been a long-felt need to reduce the cost and complexity of printer fabrication without compromising the structural strength required for the frame and lathe bed scanning assembly. However, up to this time, printer solutions have been limited to the use of conventional castings or weldments. As such, a printer frame overcoming the disadvantages of cast or welded frames would provide numerous advantages.
An object of the present invention is to provide a reinforced sheet metal body that combines the print engine chassis and machine frame into a single, rigid structure. The goal is to provide a frame that is also economical and easy to manufacture.
With the above object in view, the present invention provides a printer frame for supporting an imaging drum, a printhead translation assembly, media supply components, and supporting power supply, control logic, and vacuum components. The frame comprises a skeleton structure of interlocking rigid sheet metal members and a filler material poured into the skeleton structure to provide rigidity at points where the rigid sheet metal members interlock.
According to one embodiment of the present invention, sheet metal pieces are cut to form the interlocking rigid members, having tabs and slots that allow the interlocking rigid members to be quickly assembled by hand in order to form the skeletal structure of the printer frame. Then, a filler material, preferably of castable polymer concrete, is poured into selective cavities formed within the skeletal structure formed by the sheet metal members.
According to another embodiment of the present invention, a sheet metal printer frame for supporting an imaging drum, a printhead translation assembly, and media supply components is disclosed. The printer frame comprises a base with two walls extending from the base. The walls have cavities to accept a filler material. After the filler material is poured into the cavities, the filler material hardens to form a rigid printer frame capable of supporting the imaging drum, printhead translation assembly and the media supply components.
Also disclosed is a method for fabricating a frame for a print engine. The method comprises the step of coupling first and second sheet metal members. Next a filler material is poured over specific junctions of the sheet metal members. When the filler material hardens it firmly locks the sheet metal members together in a rigid joint.
An advantage of the present invention is that individual interlocking rigid sheet metal members can be modified in order to change the design of the printer frame, even to modify the size or configuration of the overall frame structure. This contrasts with methods using a casting, which cannot be easily modified or scaled dimensionally. This advantage is particularly beneficial when there is a need to adjust the frequency response of a structure to compensate for vibration effects, for example.
Another advantage of the present invention is that an individual interlocking rigid member can be fabricated to allow its use with a number of different printer configurations. By providing alternate slot and tab features on a rigid member, a designer can allow its use in a number of different ways, as assembled. This results in potential cost savings, cutting down the number of parts that would be needed to support multiple printer configurations.
Another advantage of the present invention is that a castable filler can be selected having optimal properties for adhesion, structural strength, and vibration damping, as well as thermal expansion characteristics closely matched to those of the surrounding metal structure.
Yet another advantage of the present invention over welded frames is the elimination of dip or chemical finishing of a large frame, as is needed following welding. An unwanted after-effect of dipping is trapping of residual fluid in the frame structure, particularly unsuitable for precision devices such as the imaging system of the present invention.
A further advantage of the present invention is that parts can be fixed in place and added to a printer frame during assembly, at the time the castable polymer filling is applied. This reduces costs over machining and allows changes to be easily incorporated into the design.
An additional advantage of the present invention is provided by the use of magnets in place of standard hardware. This allows assembly of a frame without tools.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings.